Modern agriculture, including silviculture, often requires the planting of large numbers of substantially identical plants genetically tailored to grow optimally in a particular locale or to possess certain other desirable traits. Production of new plants by sexual reproduction can be slow and is often subject to genetic recombinational events resulting in variable traits in its progeny. As a result, asexual propagation has been shown for some species to yield large numbers of genetically identical embryos, each having the capacity to develop into a normal plant. Such embryos must usually be further cultured under laboratory conditions until they reach an autotrophic “seedling” state characterized by an ability to produce their own food via photosynthesis, resist desiccation, produce roots able to penetrate soil and fend off soil microorganisms.
Some researchers have experimented with the production of artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seedcoat, such as those disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seedcoat, a synthetic gametophyte and a plant embryo. Typically, the seedcoat is a capsule having a closed end and an open end. The synthetic gametophyte is placed in its liquid phase within the seedcoat, such that the gametophyte substantially fills the seedcoat. A cotyledon restraint may then be centrally located within the synthetic gametophyte. The cotyledon restraint includes a centrally located cavity extending partially through the length of the cotyledon restraint and sized to receive the plant embryo therein. The plant embryo is subsequently deposited within the cavity of the cotyledon restraint cotyledon end first. The plant embryo is typically sealed within the seedcoat by at least one end seal.
While prior manufacturing methods have been successful in producing manufactured seeds, the process is not without its problems. For example, one problem that currently exists occurs during the gametophyte filling stage. When filling the seedcoat with gametophyte, it is necessary to leave an appropriately sized space or gap between the surface level of the gametophyte and the top edge of the seedcoat. This space enables a sufficient seal to be formed at the end of the seedcoat, for example, by a quantity of wax, subsequent to the placement of the plant embryo.
However, it has been recognized by the inventor of the present invention that the space or gap formed between the surface level of the gametophyte and the top edge of the container after filling the seedcoat with a predetermined quantity of gametophyte using the prior art process varies from seedcoat to seedcoat, often causing an insufficient space to properly seal the end of the seedcoat. This variation in the amount of space left unoccupied at the top of the seedcoat during the filling stage is due, in particular, to inconsistencies in the manufacturing process of the seedcoat. Specifically, the seedcoats are made from tubular material whose inner diameter is not precisely controlled during the manufacturing process. When using this tubular material for making manufactured seedcoats, the tubular material is cut to precise lengths. To form a seedcoat from the cut-to-length tubular material, one end is closed, either by wax or a mechanical crimping process. Because the seedcoats have varying inner diameters and a consistent length, the volume of each seedcoat varies. Thus, using a predetermined quantity of gametophyte for each seedcoat as currently done in the prior art process sometimes causes an inaccurate level of gametophyte within a certain number of manufactured seeds, which in turn, may cause an insufficient space between the gametophyte surface and the top edge of the container. This may potentially result in improperly sealed manufactured seeds, which is costly in commercial applications.